Evaluation of the risk of foreign compounds depends upon understanding the enzymes involved their degradation. A set of under-studied metabolic enzymes include the epoxide hydrolases in the ?/?-hydrolase fold family. These enzymes degrade epoxides by adding water. Some epoxides are reactive and highly mutagenic, and epoxides are commonly formed as metabolically labile functionalities by cytochrome P450s from variety of environmental chemicals. Not only are the levels of epoxide hydrolases variable in the human population, but they can be inhibited or induced by environmental chemicals and drugs. A central hypothesis is that epoxide hydrolases also have endogenous roles. We have established that the soluble epoxide hydrolase also acts on epoxides of arachidonic acid. These are key regulatory lipids. In fact, an inhibitor of the soluble epoxide hydrolase we made during the last grant period is in clinical trials to treat hypertension. Because the soluble epoxide hydrolase is involved in the regulation of blood pressure, inflammation and pain, it additionally represents a novel target for the action of xenobiotics. Similarly, inhibition of the microsomal epoxide hydrolase leads to acute xenobiotic toxicity. The knowledge of ?/?-fold enzymes will be expanded by completing two major objectives, and the tools developed here are critical to test a series of hypotheses regarding the endogenous role of the soluble epoxide hydrolase. Objective I addresses the structure and fundamental biochemistry of epoxide hydrolases with a major emphasis on the less studied soluble form. Objective II continues the development of a metabolomic profiling system to examine biologically active lipids in the arachidonate cascade and related pathways. Using this analytical platform as well as potent inhibitors and inducers of the enzyme, the role of the soluble epoxide hydrolase as a key enzyme in the arachidonate cascade and thus regulation of inflammation and pain will be evaluated. Along with 15% of the world's pharmaceuticals, common herbicides and personal care products are also known to act on the arachidonate cascade. For example we have found the common soap anti microbial, triclocarban, is a potent inhibitor of the soluble epoxide hydrolase and the endogenous peptide angiotensin along with PPAR? agonists are inducers. By addressing our objectives, knowledge will be expanded on the biochemistry and role in xenobiotic metabolism of epoxide hydrolases. The hypothesis of endogenous roles for epoxide hydrolases will be tested and the arachidonate cascade evaluated as a site of action for xenobiotics and nutraceuticals.